The present invention relates generally to a giant magnetoresistive sensor for use in a magnetic read head. In particular, the present invention relates to a giant magnetoresistive read sensor having an enhanced giant magnetoresistive response and a reduced giant magnetoresistive dependence on cap layer thickness.
Giant magnetoresistive (GMR) read sensors are used in magnetic data storage systems to detect magnetically-encoded information stored on a magnetic data storage medium such as a magnetic disc. A time-dependent magnetic field from a magnetic medium directly modulates the resistivity of the GMR read sensor. A change in resistance of the GMR read sensor can be detected by passing a sense current through the GMR read sensor and measuring the voltage across the GMR read sensor. The resulting signal can be used to recover the encoded information from the magnetic medium.
A typical GMR read sensor configuration is the GMR spin valve, in which the GMR read sensor is a multi-layered structure formed of a nonmagnetic spacer layer positioned between a ferromagnetic pinned layer and a ferromagnetic free layer. When the pinned layer is deposited prior to the deposition of the free layer, the configuration is known as a bottom spin valve (BSV). The magnetization of the pinned layer is fixed in a predetermined direction, typically normal to an air bearing surface of the GMR read sensor, while the magnetization of the free layer rotates freely in response to an external magnetic field. The resistance of the GMR read sensor varies as a function of an angle formed between the magnetization direction of the free layer and the magnetization direction of the pinned layer. This multi-layered spin valve configuration allows for a more pronounced magnetoresistive effect, i.e. greater sensitivity and higher total change in resistance, than is possible with anisotropic magnetoresistive (AMR) read sensors, which generally consist of a single ferromagnetic layer.
A pinning layer is typically exchange coupled to the pinned layer to fix the magnetization of the pinned layer in a predetermined direction. The pinning layer is typically formed of an antiferromagnetic material. In antiferromagnetic materials, the magnetic moments of adjacent atoms point in opposite directions and, thus, there is no net magnetic moment in the material.
A seed layer is typically used to promote the texture and enhance the grain growth of the pinning layer consequently grown on top of it. The seed layer material is chosen such that its atomic structure, or arrangement, corresponds with the preferred crystallographic direction of the magnetization of the pinning layer material.
One principal concern in the performance of GMR read sensors is the maximum absolute change in resistance of the GMR read sensor, which directly affects the GMR ratio. GMR ratio (the maximum absolute change in resistance of the GMR read sensor divided by the resistance of the GMR read sensor multiplied by 100%) determines the magnetoresistive effect of the GMR read sensor. Ultimately, a higher GMR ratio yields a GMR read sensor with a greater magnetoresistive effect which is capable of detecting information from a magnetic medium with a higher linear density of data.
A recent method of increasing the GMR ratio in bottom spin valves is through the use of an oxide cap layer. Typically, an oxide cap layer is deposited on top of the free layer to function as a reflective layer for increasing the electron specular scattering at the free layer/cap layer interface. This increases the change in resistance of the bottom spin valve and thus increases the GMR ratio. In practice, however, oxide cap layers are not structurally perfect but instead contain pinholes and other material defects. If the oxide cap, layer is too thin, portions of the free layer will be exposed and become oxidized. This causes both the interlayer coupling field and the coercivity of the free layer to increase, requiring a greater applied magnetic field from a magnetic data storage medium to produce a given giant magnetoresistive response. If the oxide cap layer is too thick, there is a significant drop in the GMR ratio, and the interlayer coupling field becomes very high and oscillates with the oxide cap layer thickness. Therefore, the properties of a bottom spin valve capped with a single oxide layer are very sensitive to the thickness of the oxide cap layer.
Accordingly, there is a need for a GMR read sensor having an enhanced giant magnetoresistive response and a reduced giant magnetoresistive dependence on cap layer thickness.
The present invention is a giant magnetoresistive spin valve for use in a magnetic read head. The spin valve includes a ferromagnetic free layer and a multilayer cap layer. The free layer has a rotatable magnetic moment. The multilayer cap layer is positioned adjacent to the free layer for increasing electron specular scattering of the free layer. In one preferred embodiment, the multilayer cap layer includes at least one oxide layer positioned adjacent to the free layer, and at least one conductive layer positioned adjacent to the oxide layer.